Hi sunder,
Few tips to increase ur GMAT Mock test score and increasing confidence
1) Take the practice tests in a similar Test day setup. Be in a separate room and have a mindset like a test day
2) Dont be casual thinking that it is jus a test drill
3) Before taking the test refresh all the formulas and notes u would have written for ur weaker sections
4) Dont be disturbed by phone calls or other people atleast for 3 hours
5) Dont take the test if u r in a stress, feeling fatigue, or in any unpleasant situation. Have a cool mind and give 100% efforts and seriousness
I am sure u will score a min of 700+ in ur GMATprep test. These scores gives u a lot of confidence in ur test day but it should not be overconfidence
Hope this helps you for improving ur confidence level.